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    A NEW NONLINEAR ANALYTICAL CONTROL OF THE HUMAN KNEE JOINT OF PARAPLEGIC PATIENTS UNDER INITIAL KNEE ANGLE UNCERTAINTIES
    (Cefin Publishing House, 2024) Al-Bakri, Fawaz F.; Khafaji, Salwan Obaid Waheed; Ali, Hasan H.; Al Juboori, Ameen M.; Cihan, Ibrahim H.
    The prolonged sitting for disabled patients can cause several health problems such as muscle wasting, bedsores, and pain. The majority of these disabled people are paraplegic patients that the activities of their muscles can effectively increase due to knee position training. In this work, a new analytical methodology for controlling the human knee position is emphasized. The knee angle profile is parameterized using seven-term exponential function. These seven coefficients are computed by fulfilling the initial and final states for knee angle, knee velocity, and electrical torque. Then, the analytical pulse width will be used to simulate the nonlinear knee dynamic system achieving the steady-state knee position with fast settling time (0.48 sec) and small overshoot (3.22%). Eventually, the introduced algorithm is confirmed in the presence of initial knee angle dispersions using Monte-Carlo simulation method. As a result, the nonlinear analytical control is successfully able to steer the human knee angle from the initial state to the desired state shortly with maximum overshoot of about 6.8% while including a wide range of initial knee angle deviations. © 2024, Cefin Publishing House. All rights reserved.
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    Discrete-Event Drag Modulation Aerocapture for Mars and Titan Missions
    (Amer Inst Aeronautics Astronautics, 2024) Cihan, Ibrahim H.; Al-Bakri, Fawaz F.; Kluever, Craig A.
    Aerocapture is a spaceflight maneuver that uses the atmosphere of a planet or moon to slow down a spacecraft after a single atmospheric pass and capture it into an elliptical orbit around the celestial body. This paper presents a discrete-event drag modulation method for Mars and Titan aerocapture missions. A single-stage jettison is used as a control strategy to modulate the aerodynamic drag for an aerocapture scenario. Entry corridor analysis is performed under worst-case trajectory dispersions for determining the entry flight-path angle. The jettison timing of the high-drag skirt is the single free guidance parameter that adjusts the spacecraft's trajectory during an aerocapture maneuver. A computationally simple jettison-switching guidance scheme is developed to determine when to jettison the high-drag skirt, and the result is an analytical function that represents the ballistic-coefficient switching curve. The proposed discrete-event drag-modulation strategy is extensively tested using four entry vehicles and three target orbits for Mars and Titan aerocapture scenarios. Monte Carlo simulations show that the simple switching-curve guidance provides performance metrics (apoapsis targeting errors and postexit impulsive maneuvers) that are essentially equal to the performance of more computationally burdensome guidance methods such as an onboard numerical predictor-corrector scheme.